The distal radioulnar joint is a “shallow socket” ball joint. The radius articulates in pronation and supination on the distal ulna. The ulna, a relatively straight forearm bone linked to the wrist, translates dorsal-palmarly to accept the modestly bowed radius. Since the sigmoid fossa socket in most wrists is relatively flat, ligaments are required to support the distal ulna. These ligaments include the triangular fibrocartilage (TFC), the extensor carpi ulnaris (ECU) subsheath, and the ulnar collateral ligament complex. The stabilizing elements of the triangular fibrocartilage (TFC), extensor carpi ulnaris (ECU) subsheath, and the ulnar collateral ligament complex are well recognized along with the importance of a distal ulna component (ulnar head) for transfer of compressive loads between the ulnar carpus and the distal ulna across the distal radioulnar joint.
Ligament disruption, ulnar styloid fractures, and fractures into the distal radioulnar joint are common occurrences following fractures of the distal radius and other rotational instability injuries of the forearm. Fracture or dislocation involving the distal radioulnar joint often results in a loss of forearm rotation related to either instability or incongruity between the sigmoid fossa of the distal radius and the ulnar head. A variety of different fractures involving the distal radius may cause this condition including the Colles' fracture and the Galeazzi fractures. When there is loss of stability of the distal radioulnar joint, there is subsequent weakness in grip and pinch as well as potential loss of forearm rotation. Instability may also be associated with either an injury to the triangular fibrocartilage or to the ulnar styloid. As instability is present, a number of ligament reconstructive procedures have been devised to assist in treating the unstable distal ulna. Unfortunately, ligament reconstruction of the distal ulna is often incomplete in restoring stability, and joint replacement is often necessary.
Where there is an incongruity of the joint surface involving either the articulation of the ulnar head with the sigmoid fossa of the distal radius, or if there is a significant ulnar impaction syndrome between the distal articular surface of the head of the ulna and the ulna carpus, a joint replace may be necessary. Specifically, this may include either joint replacement of the distal ulna or operative procedures designed to shorten the ulna or resect all or part of the distal ulna. Unfortunately, there have been variable results associated with the partial or complete resections of the distal ulna, particularly those performed by open resection. For example, when the ulna is resected, and not replaced with a prosthesis, both instability of the wrist and “snapping” of the forearm in rotational pronation/supination may occur.
The primary indications, therefore, for reconstruction of the distal radioulnar joint by prosthetic replacement are generally related to a fracture of the distal ulna or a fracture extending into the distal radioulnar joint producing post-traumatic arthritis. Degenerative arthritis from other causes is also a primary indication. This is considered if there is associated arthritis and an ulnar shortening procedure is contraindicated. A third condition for primary ulna replacement is rheumatoid arthritis with a painful and unstable distal radioulnar joint. In these situations, prosthetic replacement of the distal ulna with soft tissue advancement may be beneficial.
A distal ulnar prosthesis is also suitable to correct a previous resection of the distal ulna that has failed. Such will be the case for 1) partial resection of the joint articular surface, or 2) complete resection of the distal ulna. When face with the failed distal ulna resection, one has options towards reconstruction without restoring the distal radioulnar joint. For example, a failed distal ulna may be corrected by a pronator quadratus interposition, or, if there has been only a partial resection, a fusion of the distal radioulnar joint combined with a proximal pseudarthrosis.
These procedures, however, do not restore the normal distal radioulnar joint function of motion or load transfer and are also associated with some drawbacks. For example, there are difficulties in retaining stability of the distal ulna and proximal impingement of the ulna on the distal radius. In addition, movements of the forearm causes a slipping movement of the metallic prosthesis on the ulna/radius bone that may cause to prosthesis wear. There is, therefore, a need in the art for intraosseous artificial prosthesis for distal radioulnar joint that is able to retain stability of the distal ulna and proximal impingement of the ulna on the distal radius and prevents the prosthesis wearing during forearm motions.